Through the years, polyurethane foams have enjoyed widespread commercial acceptance. Procedures for producing both flexible and rigid foams are well-known. Flexible foams are used in furniture cushions, mattresses, carpet underlays, etc.; while rigid foams have been used primarily in thermal and acoustical insulation applications.
Polyurethane foams are typically prepared by reacting polyisocyanate and polyol in the presence of catalyst, emulsifying agents, and other additives such as foaming agents. Polyols generally used include synthethic materials such as polyethers and polyesters as well as natural polyols such as castor oil. A common characteristic of foams based on polyurethane is their poor resistance to heat and flame. This low heat and flame resistance is due, to a large degree, to the polyol component used in the foam's formulation. This characteristic of polyurethane foams is particularly disconcerting because many uses for these materials are in residential environments and structural applications.
Various approaches for improving the heat and flame resistance of polyurethanes have been tried. A principal approach has been to introduce flame and heat depressants or inhibitors based on halogen, phosphorous or nitrogenous compounds into the foam. While such materials do reduce polyurethane flammability, they unfortunately tend to exacerbate the evolution of toxic gases under high temperature decomposition conditions. For this reason, there is a strong need in the art for alternate techniques for improving the heat and flame resistance of polyurethanes.
It is well-known that phenolic resins have good heat and flame resistance. In Davis et al U.S. Pat. No 3,598,771 a method for incorporating such materials in polyurethane foams is disclosed as a way of upgrading the heat and flame resistance of polyurethanes. According to this patent, conventional novolac-type phenolic resins can be substituted for or preferably used in combination with the polyol component. The novolac resin is prepared in the conventional fashion to yield a thermoplastic polymer; i.e., a molar excess of phenol is reacted with formaldehyde (eg. 0.7-0.85 mole formaldehyde per mole phenol) under atmospheric reflux conditions in the presence of an acidic catalyst. The novolac resin is thereafter reacted with a polyisocyanante in the presence of emulsifier, blowing agent and catalyst. While significantly improved heat and flame resistance is described, foam production and properties are unavoidably compromised. Novolac resins are normally produced as solid, thereby making them difficult to disperse with polyisocyanate in the time necessary for good foam production. Consequently, the bulk of the novolac resin acts as a flame retardant filler rather than reacting with isocyanate. As a way of upgrading foam properties, novolac resin is blended with a conventional polyol, e.g., a polyether or a polyester. Unfortunately, this compromises the heat and flame resistance of the urethane produced.
It would be of great value, therefore, to provide a new class of phenolic-aldehyde based polyols which can be used to improve the heat and flame resistance of polyurethanes, while avoiding the above noted disadvantages of thermoplastic novolac resins.
It is an important object of this invention to produce a phenolic-aldehyde based resinous thermosetting polyol that can be reacted with isocyanates to produce urethane polymers with improved heat and flame resistance.
It is another object of this invention to produce a phenolic-aldehyde based resinous thermosetting polyol that is liquid under standard urethane reaction conditions.
It is a further object of this invention to produce a phenolic-aldehyde based thermosetting resinous polyol that has a high, controlled hydroxyl number, above about 400, making it ideally suited for urethane manufacture by reaction with isocyanates.
It is still another object of this invention to provide a phenolic-aldehyde based thermosetting polyol that can also be used as a plasticizer for conventional phenolic resins.